Rufinus: Preface to the Sayings of Xystus
- "I translated into Latin in a very open and plain style the work of Xystus, who is said to be the same man who at Rome is called Sixtus, and who gained the glory of being both bishop and martyr."
- http://www.ccel.org/ccel/schaff/npnf203.vi.xv.html

The Ecole Glossary
- Two brief paragraphs on the papacy and martyrdom of St. Sixtus II.
- http://www2.evansville.edu/ecoleweb/glossary/sixtusii.html

Catholic Encyclopedia
- Pope St. Sixtus II, also spelled Xystus. This is the St. Sixtus who is commemorated in the Eucharistic Prayer. Pope who was one of the first martyrs of the Valerian persecution, in 258.
- http://www.newadvent.org/cathen/14031c.htm

Popes Through the Ages
- Account of the pontificate of Pope St. Sixtus II, from the book by Joseph Brusher.
- http://www.cfpeople.org/Books/Pope/POPEp24.htm